A probe is utilized to measure electrical characteristics of a tiny electronic component (for example, a semiconductor device or a thin film transistor array in a liquid crystal display panel). A person who is skilled in the art realizes that a thin film transistor array (TFT Array) has a plurality of gate lines and signal lines that are respectively connected to a plurality of test pads for exchanging signals with an external electronic system. Electrical signals are inputted into the TFT arrays through the aforementioned test pads to implement a testing process. Then, the testing results are outputted to the external electronic system through the aforementioned test pads to detect the performance of electrical characteristics of the display panel or detect any defect thereof.
In the mean-time, a plurality of probes are arranged on a flexible printed circuit (FPC) board to form a “Probe Block” or a “Probe Card”. The probes actually contact the test pads of the circuits under test (such as the TFT array) in a testing process so that the circuits can be tested through the test pads with external components or systems.
Currently, with increasing pixels in the liquid crystal display panels, the distances between the adjacent test pads are shortened, as well as the sizes of the test pads become smaller. In order to contact easily, the structure of a probe is fabricated as a bump being coupled to one end of a lead. The bump is connected with one of the test pads of the circuits under test, so that the electrical signals of the circuits (such as the TFT array) can be outputted through the lead. In addition, due to the shortened distances between the test pads, the distances between the bumps of the probes are also shortened. Therefore, the bumps of the probes must be precisely arranged when contacting the test pads so as to avoid a short circuit or electrical disturbances generated therebetween.
Please refer to FIG. 1. FIG. 1 is a top view illustrating a probe block fabricated by conventional art. FIG. 1 illustrates the structure of a probe block 100, wherein the probe block 100 includes a plurality of metal wires 110 being disposed on a flexible printed circuit board 105. A plurality of metal bumps 120 being disposed on the metal wires 110, and the metal bumps being arranged into staggered rows as shown in FIG. 1. Such an arrangement is designed to increase the distance between the adjacent metal bumps 120, but the metal bumps can also be aligned into a single row.
Because the metal bumps 120 of the probe block 100 have to be arranged closely, the conventional art utilizes a photolithography to fabricate the metal wires 110 and the metal bumps 120 on the flexible printed circuit board 105. The metal wires 110 are connected to the metal bumps 120, and the metal bumps 120 are utilized to contact the test pads. The fabrication method includes the steps as follows: forming a plurality of metal wires 110 which are disposed on a flexible printed circuit board 105 by a first photolithography process; and forming a plurality of metal bumps 120 which are disposed on the metal wires 110 by a second photolithography process.
However, in the exposure process of the second photolithography process in fabricating the metal bumps 120, the flexible printed circuit board 105 has to be aligned and fixed by the clamping apparatuses. Moreover, due to the flexible characteristic of the flexible printed circuit board 105, the flexible printed circuit board 105 is deformed after it is fixed by the clamping apparatuses. Still, the aligned position could be dislocated in the second photolithography process, and the metal bumps 120 could be inaccurately formed on the metal wires 110 thereof.
Please refer to FIG. 2. FIG. 2 is a cross-sectional view illustrating a probe block fabricated by conventional art when contacting the test pads. FIG. 2 illustrates the shortcomings of testing by using the probe block 100 which is fabricated by conventional art. The dislocated distances between the metal bumps 120 and the metal wires 110 give rise to a concern that the probe block 100 must be aligned accurately to a plurality of test pads 210 when utilized in actual tests. As a result of the aforementioned, the probe block 100 is only allowed to dislocate a short distance. Moreover, the dashed lines in FIG. 2 represent the limits of the positions that each of the metal bumps 120 is correctly measured, and the limits are indicated by the arrows shown in FIG. 2. In other words, the margin is very narrow when using the conventional probe block 100 to test. In addition, when the dislocated distances of the positions are greater than the margin, the metal bumps 120 on the probe block 100 will contact the other test pads 210, thus causing detection errors.
Moreover, the metal bumps that are fabricated by conventional art can not be accurately formed on the metal wires, and there are gaps existing between the metal bumps and the metal wires. Thus, when the metal bumps contact the test pads, the metal bumps may be cracked from the gaps therein by lateral forces caused by the metal bumps being out of alignment with the test pads, and thus the probes become unserviceable. Consequently, the probes' durability can not be improved, and even worse, the aforementioned occurrence might give rise to false test results.
Therefore, fabricating accurate and durable probes to test liquid crystal display panels is urgently needed to be proposed. More importantly, a more efficient probe fabrication method is needed to be proposed in order to resolve the aforementioned issues.